What can go wrong with HashMap if all keys have the same hash code? Why will search slow down?

If all keys in a HashMap have the same hash code, then all elements will fall into the same bucket. As a result, the structure, which is supposed to provide quick access (usually O(1)), degrades to a linear search through the chain of elements (O(n)).

Why does this happen:

• The hash function distributes keys across buckets for quick access.
• With the same hash code, all keys end up in one bucket.
• When searching for a key, it has to be compared sequentially with each element in that bucket.

This leads to a significant slowdown of get, put, and remove operations, especially with a large number of elements.

Example:

Map<String, String> map = new HashMap<String, String>() {
    @Override
    public int hashCode() {
        return 42; // same hash for all keys
    }
};
// All keys will be in one bucket, search will be linear